The present invention relates to twin rotor blowers/compressors, twin rotor expanders, etc. Such twin rotor blowers/compressors have been used for supercharging internal combustion engines (e.g., Diesel cycle engines, Otto cycle engines, etc.). When used on internal combustion engines, such twin rotor blowers/compressors may be a component of a forced induction system that supplies air or an air/fuel mixture to the internal combustion engine. Such forced induction systems supply the internal combustion engine with the air or the air/fuel mixture at a higher pressure than atmospheric pressure. In contrast, naturally aspirated internal combustion engines are supplied with air or an air/fuel mixture at atmospheric pressure. By supplying pressurized air or a pressurized air/fuel mixture to the internal combustion engine, the engine is supercharged. The twin rotor blowers/compressors may be known as positive displacement superchargers. Such positive displacement superchargers displace a given volume of gas for every revolution of an input shaft at a given pressure and a given temperature. In contrast, certain other superchargers may be non-positive displacement superchargers.
The twin rotor blowers/compressors may take a form of a Roots-type device, a form of a screw compressor, etc. The Roots-type device may have a pair of rotors that intermesh with each other. In particular, each of the rotors may define a similar plurality of lobes with valleys between adjacent lobes. The lobes and valleys of the pair of rotors may be mirror images of each other (e.g., if helically twisted). The lobes and valleys of the pair of rotors may be identical to each other (e.g., if straight along an axial direction of the rotor). The lobes and valleys may be defined by alternating tangential sections of hypocycloidal or hypocycloidal-like curves and epicycloidal or epicycloidal-like curves. When each of the pair of rotors is spun, fluid is trapped in the valleys and bounded by the adjacent lobes and walls of a housing and carried from an intake side to an exhaust side of the Roots-type device. The twin rotor blowers/compressors (e.g., the Roots-type device) may move the fluid from the intake side to the exhaust side without compression until the fluid is exposed to the exhaust side (e.g., an exhaust port). As the fluid is forced out of the exhaust port, it may be compressed.
The screw compressor (e.g., a twin-screw type supercharger) may have a pair of rotors that intermesh with each other. In particular, the pair of rotors may include a male rotor and a female rotor that intermesh with each other. The male rotor and the female rotor may have different numbers of lobes or a same number of lobes. A working volume may be defined as an inter-lobe volume between the male and the female rotors. When each of the pair of rotors is spun, fluid is trapped in the working volume bounded by the adjacent lobes and walls of a housing and carried from an intake end to an exhaust end of the screw compressor. The working volume may be larger at the intake end. The working volume may decrease along an axial length of the rotors toward the exhaust end. Fluid is drawn in at the intake end of the rotors between the male and female lobes. A corresponding reduction in the working volume toward the exhaust end may result in compression of the fluid that is trapped in the working volume. For example, at the intake end, the male lobes of the male rotor (and corresponding valleys of the female rotors) may be larger than corresponding female lobes of the female rotor (and corresponding valleys of the male rotors), and at the exhaust end, the male lobes (and corresponding valleys of the female rotors) may be smaller than corresponding female lobes (and corresponding valleys of the male rotors). Thus, relative sizes of the male and female lobes may reverse proportions along axial lengths of both of the rotors (e.g., the male lobes become larger and the female lobes become smaller). The increase in volume of the female lobes may result in a reduction in volume of the fluid carrying cavity and thereby cause the compression of the fluid before the fluid carrying cavity is in fluid communication with the exhaust end.
Other methods of reducing the working volume toward the exhaust end may be used. In certain embodiments, a screw-compressor like device may not necessarily reduce the working volume toward the exhaust end.
An example Roots-style supercharger is disclosed at U.S. Pat. No. 7,866,966, assigned to the assignee of the present disclosure, and incorporated herein by reference in its entirety. Another example Roots-style supercharger is disclosed at U.S. Pat. No. 4,828,467, also assigned to the assignee of the present disclosure, and also incorporated herein by reference in its entirety. As such Roots-style superchargers (and other twin rotor superchargers) typically draw air in through an inlet at atmospheric pressure and deliver compressed air from an outlet to an intake manifold of the internal combustion engine at an elevated pressure, the elevated pressure from the outlet of the Roots-style supercharger (and other twin rotor superchargers) typically tends to leak back across clearances within the supercharger. Such clearances may be between lobes of a pair of rotors within the supercharger. Clearances may also exist between tips of the lobes of the rotors and a housing of the supercharger. Clearances may further exist between an end of the rotors of the supercharger and corresponding surfaces of the housing. Such clearances are often determined, at least in part, by manufacturing tolerances of the rotors and the housing of the supercharger. For example, a Roots-style supercharger made with a collection of components at a minimum material condition with respect to the manufacturing tolerances will have leakage rates higher than another Roots-style supercharger assembled from components at a maximum material condition with respect to the manufacturing tolerances. This may lead to certain Roots-style superchargers that are nominally identical having different performance characteristics that are caused by the different leakage rates. Furthermore, it is generally desired to reduce such clearances and thereby minimize leakage within the supercharger. However, increasing precision of the manufacturing tolerances may increase manufacturing costs. Furthermore, a number of different dimensions and corresponding dimensional tolerances together determine the clearances that exist at final assembly. It is desired to reduce the leakage rate within a supercharger (and other twin rotor devices) without depending upon high precision dimensional tolerances from the set of individual components in the assembled supercharger and/or twin rotor device.
Typical screw compressors have similar leakage issues caused by clearances between lobes of the pair of rotors, clearances between tips of the lobes of the rotors and a housing, and clearances between an end of the rotors and corresponding surfaces of the housing. Likewise, increasing precision of the manufacturing tolerances may increase manufacturing costs, and a number of different dimensions and corresponding dimensional tolerances together may determine the clearances that exist at final assembly. It is also desired to reduce the leakage rate within a screw compressor without depending upon high precision dimensional tolerances from the set of individual components in the assembled screw compressor.
When Roots-style superchargers or similar twin rotor devices are run in reverse (i.e., when fluid pressure and flow are converted into shaft power), a Roots-type device (and/or other twin rotor device) may serve as a Roots-style expander (and/or other twin rotor expander). Such expanders may have similar leakage issues caused by clearances between lobes of the pair of rotors, clearances between tips of the lobes of the rotors and a housing, and clearances between an end of the rotors and corresponding surfaces of the housing. It is also desired to reduce the leakage rate within a Roots-style expander without depending upon high precision dimensional tolerances from the set of individual components in the assembled Roots-style expander.
Similarly, when screw compressors or similar devices are run in reverse (i.e., when fluid pressure and flow are converted into shaft power), a screw-type device may serve as a screw expander. Such screw expanders may have similar leakage issues caused by clearances between lobes of the pair of rotors, clearances between tips of the lobes of the rotors and a housing, and clearances between an end of the rotors and corresponding surfaces of the housing. It is also desired to reduce the leakage rate within a screw expander without depending upon high precision dimensional tolerances from the set of individual components in the assembled screw expander.